High wet strength paper and its preparation



Patented Aug. 3, 1954 HIGH WET STRENGTH PAPER AND ITS PREPARATION Donald R. Spear, Rochester, N. Y., assignor to Eastman Kodak Company, Rochester, N. Y., a corporation of New Jersey No Drawing. Application December 1, 1950, Serial No. 198,733

4 Claims.

1 This invention relates to the improvement of physical properties of paper of the high wet strength type by adding to a pulp slurry melamine-formaldehyde resin and oxidized guar prior to forming the paper web on the felt or wire of a paper machine.

In certain types of uses such as the base for photographic paper it is desirable that the paper have high wet strength, fold endurance, resistance to liquid penetration and dry bursting strength and that the rate of liquid absorption be less than is ordinaril encountered in paper. It has been previously recognized in U. S. appli cation Serial No. 532,299 of Fred W. Boughton, filed April 22, 1944, now Patent No. 2,548,513, that the addition of an aqueous acid solution of melamine-formaldehyde resin to a pulp slurry will increase the wet strength of the paper formed therefrom. It is also known that the mucilage from the seeds of guar when added to pulp slurry will impart an increased wet and dry strength to the finished paper. I have found, however, that by incorporating melamine-formaldehyde resin and oxidized guar in a pulp slurry prior to the preparation of paper therefrom, that these materials exert a combined effect greater than would be expected so that a paper having a higher wet strength, fold endurance, dry burst strength and resistance to liquid penetration is obtained by the use of either of these materials alone.

The melamine-formaldehyde resin is that which is ordinarily employed as a beater sizing in the preparation of high wet strength paper and is readily available on the market such as under the trade name Parez 607. The melamine-formaldehye resin is added in the form of a solution in dilute hydrochloric acid. Oxidized guar is the oxidation product of the mannogalactan mucilage from seeds of guar. One method by which this oxidized guar can be obtained is by first slowly adding the guar to an aqueous borax solution followed by the addition thereto of a solution of sodium hypochlorite and allowing the reaction to continue until substantially all of the hypochlorite is consumed. Oxidized guar is available on the market under the trade name Royal Lycoid.

It is preferred in making paper in accordance with my invention that there be incorporated in the pulp suspension in the beater one of the usual beater sizings which suspension is acidified to a pH of 4 to 5 by the addition of an acidifying agent such as aluminum chloride or aluminum sulfate, the former being preferred, The

usual beater sizing materials are rosin, hydro genated rosin or stearic acid which has been saponified with caustic soda or the like. Ordinarily the size may be prepared from the rosin, hydrogenated rosin, or stearic acid by treating the material with one-third of its weight of caustic soda. The soap thus formed can be employed in the beater in any dilution desired. It is preferred that the amount of caustic soda be kept to a minimum as otherwise larger proportions of acid in the beater sizing operation would be necessary. After the beater sizing and the acid imparting material has been thoroughly incorporated in the pulp there is then added thereto the melamine-formaldehyde resin and the oxidized guar. These materials can be added either simultaneously or one can be added shortly prior to the other. This addition may take place in the beater proper or the beating operation can be completed and the pulp may then be put through the Jordan in which the addition of the melamine-formaldehyde resin and the oxidized guar may be made. After this operation the paper stock is then ready for deposit on the wire of the paper machine wherein paper is prepared therefrom.

The proportions of the melamine-formaldehyde resin and the oxidized guar which have been found to be the most useful lie within the range of 1-2% of the former and /.;-2% of the latter, these percentages being based on the bone dry weight of the pulp. For instance good results have been obtained using 2% of each, 2% of the melamine-formaldehyde resin and 1 of the oxidized guar, 1% of the resin and of the oxidized guar and 2% of the resin and of the oxidized guar. If one of these constituents is to predominate, it is preferable that the melamine-formaldehyde resin be that predominating constituent.

The fibers appear to take up the resin and the oxidized guar readily and thus these proportions also carry over to the paper prepared in accordance with my invention. The following examples illustrate my invention:

Example I 141 parts of an aqueous solution of sodium stearate which stoiohiometrically contains approximately 2% stearic acid was added to 6,000 parts of a slurry of pulp and water containing parts of dry pulp. This mass was agitated for a minute or two whereupon an aqueous solution of aluminum chloride of 14% strength was added in sufficient amount to depress the pH of the slurry to approximately 4.2.

After agitating the mass for a few minutes 20 parts of a 7.5% solution of melamineformalde hyde resin in dilute aqueous hydrochloric acid was added, The mixture was placed in a Noble Wood proportioner and sufficiently diluted that one quart of the slurry will form a sheet having dimensions of 8" x 8" weighing 2.5 grams after pressing between two pieces of felt to approximately 35% moisture content and drying on a rotary dryer at 200-210 F. for 3 to 4 minutes. This paper was prepared to be used for comparison for papers in which a mixture of melamine-formaldehyde resin and oxidized guar is used.

Example II The procedure of Example I was repeated except that 101 parts of a hot aqueous 1% solution of oxidized guar was employed instead of the melamine-formaldehyde resin solution. This procedure was also for the purpose of preparing a product for comparison with the products in accordance with my invention.

Example III The procedure of Example I was repeated except that after the addition of the melamineformaldehyde resin and approximately 5 minutes of agitation, 101 parts of a 1% solution of oxidized guar was added to the mass and thoroughly incorporated therein.

Example IV Example 11 was repeated except that after the addition of the oxidized guar solution and agitation for approximately 5 minutes, 20 parts of a 7.5% solution of melamine-formaldehyde resin in aqueous hydrochloric acid was incorporated and the paper sheet was then formed.

Example V Example I was repeated except that instead of adding 20 parts of the melamine-formaldehyde resin solution, 101 parts of a 1% solution of oxidized guar and 20 parts of a 7.5% solution of melamine-formaldehyde resin were added simultaneously to the pulp mass and thoroughly incorporated therein whereupon the mass was diluted and paper was formed therefrom.

The various papers prepared by the procedure of Examples I to V were subjected to a series of physical tests and the results obtained indicate that the combination of the malamine-formaldehyde resin and the oxidized guar therein give desirable physical properties which could not be attained by the use of either one of these add tions alone. The results in the various physical tests were as follows:

The papers before testing were first conditioned for two hours at approximately 73 F. and approximately 50% relative humidity. This conditioning is in accordance with Tappi specification 402M4l.

The testing as regards folds was carried out by placing strips of conditioned paper having a width of 15 mm. and a length of at least 6 inches in an M. I. T. folding endurance tester. The tester subjects the samples to 180 double folds per minute while under a constant load of l kilogram. The results are read directly from a counter and expressed as number of double folds.

The .wet strength is determined in accordance with Tappi specification 403M41. In these tests the samples of paper were soaked in distilled water at room temperature for two hours. The bursting strength is then measured on a Minden paper tester. The results are expressed in pounds per square inch.

The Mullen value was determined in accordance with Tappi specification 403M41. Samples of the conditioned paper were placed in an automatic Mullen paper tester and were subjected to increasing hydrostatic pressure over an area of one square inch. The results are expressed directly in points, one point being approximately one pound,

The valley penetration recorded in seconds was obtained by mounting a 2" square sample of conditioned paper between two wooden blocks that have been drilled to allow an electrolyte (516 ml. distilled water, 24 g. of NaCl, 60 ml. glycerine) to contact both sides of the paper simultaneously over a circular area that is one inch in diameter. A potential is applied that allows 200 milliarnperes of current to flow when no paper sample is present. When a paper sample is mounted in the blocks the time in seconds is noted from the moment the electrolyte is first brought into contact with the paper sample until 160 milliamperes of current flows through the sample. This time in seconds is the valley penetration value of the paper.

The Cobb size was determined in accordance with Tappi specification T441M45. This value is determined as follows:

An open cylinder with cross-sectional area of 100 cm. is clamped over the sample of conditioned paper to be tested. A piece of felt under the sample acts as a seal. 50 ml. of distilled water is poured in the top of the cylinder and allowed to remain in contact with the surface of the paper sample a predetermined length of time. In this case, 2 minutes. At the end of the period the water is poured out of the cylinder, the paper sample blotted to remove excess moisture and the sample weighed. The difference in wet and dry weight is expressed in grams and is a measure of the sizing of the paper.

Further examples involving the preparation of a high wet strength paper in accordance with my invention are as follows, in every case 6,080 parts of aqueous pulp slurry containing 2 pulp being used which slurry has been beaten to a Williams slowness of 20 to 25 seconds.

Example VI The procedure described was repeated but the additions to the pulp were as follows:

141 parts 1.92% sodium stearate size solution 85 parts 14% AlCla solution 36 parts 7.5% melamine-formaldehyde solution The values obtained upon testing the paper were as follows:

Wet Valley Cobb Fold Mullen Strength Penetration Size Example VII In this example and those following, the materials listed were added to the pulp in the beater or after. The additions to the pulp in the beater were as follows:

141 parts 1.92% sodium stearate size solution 85 parts 14% A1013 solution 36 parts 7.5% melamine-formaldehyde solution 67.5 parts 0.5% oxidized guar solution The last two items ware added simultaneously. Paper was prepared and the values obtained were:

Wet Valley Cobb Fold Mullen Strength Penetration Size Example VIII 141 parts 1.92% sodium stearate size solution 85 parts 14% A101;

4.5 parts 7.5% melamine-formaldehyde solution 540 parts 0.5% oxidized guar solution Values obtained from the paper prepared were:

Wet Valley Cobb Mullen Strength Penetration Size Example IX 141 parts 1.92% sodium stearate size solution 85 parts 14% A1013 540 parts 0.5% oxidized guar solution 141 parts 1.92% sodium stearate size solution 85 parts AlCla The values obtained from the paper resulting were:

Wet Valley Cobb F 01d Mullen Strength Penetration Size The following examples serve to demonstrate that with the exception of fold, little difierence is found whether the melamine-formaldehyde resin and the oxidized guar are added simultaneously or one is added following the other.

Example XI There was added to the pulp in the beater:

141 parts 1.92% sodium stearate size 85 parts 43% A1013 solution 18 parts 7.5% melamine-formaldehyde solution 270 parts 0.5% oxidized guar solution The last two items were added simultaneously.

The values obtained from the paper resulting were:

. Wet Valley Cobb Told Mullen Strength Penetration Size Example XII There was added to the pulp suspension:

141 parts 1.92% sodium stearate size parts 14% A1012 solution 270 parts 0.5% oxidized guar solution The suspension was agitated for 3 minutes and there was then added 18 parts of melamineformaldehyde resin solution. The values obtained from the paper resulting were:

Wet Valley Cobb Fold Mullen Strength Penetration Size Example XIII In this case there was added to the suspended pulp in the beater:

141 parts 1.92% sodium stearate size 85 parts 14% AlCh solution 18 parts 7.5% melamine formaldehyde solution The suspension was agitated 3 minutes and there was then added 270 parts 0.5% oxidized guar solution. The values obtained from the paper resulting were:

Wet Valley Pen- Cobb F 01d Mullen Strength etration Size The following examples also illustrate the value of the addition of both melamine-formaldehyde resin and oxidized guar.

Eacample XIV There was added to the pulp suspension in the beater 141 parts 1.92% sodium stearate size and sufficient aluminum chloride to inject a pH of 4. Paper was formed therefrom.

Wet Valley Pen- Cobb Fold Mullen Strength etration Size Example XV To the pulp suspension in the beater there was added:

141 parts of 1.92% sodium stearate size Aluminum chloride to impart a pH of 4 and 18 parts of 7.5% melamine-formaldehyde resin solution Paper was formed therefrom.

Wet Valley Pen' Cobb Fold Mullen Strength etratlon Size 7 Example XVI To the pulp suspension in the beater was added 141 parts of 1.92% sodium stearate size, AlC13, to impart a pH of 4 and 101 parts of 1% oxidized guar solution. Paper was formed therefrom.

There was added to the pulp suspension in the beater:

141 parts of 1.92% sodium stearate size AlCb to impart a pH of 4 101 parts of oxidized guar solution 18 parts of melamine-formaldehyde resin solution Paper was formed therefrom.

Wet Valley Pcn- Cobb Fold Mullen Strength etration Size In Examples VI to XVII given above in every 9 case paper was prepared and subjected to tests which have been described herein and the values obtained are listed in those examples.

The pulp which is employed in preparing paper in accordance with my invention is preferably a high alphaoellulose pulp such as may be obtained by preparing pulp by a sulfite process and then subjecting it to defining steps as is known in the art for preparing high alphacellulose woodpulp. It is to be understood, however, that my invention is not confined to that type of pulp as the invention that I have described herein is useful for improving the properties of papers generally as regards their strength and resistance to the efiects of moisture, either water vapor or in liquid form.

I claim:

1. A method of preparing paper adapted for as a base for photographic paper which includes adding to the pulp slurry from which the paper is prepared melamine formaldehyde resin and oxidized guar prior to forming the paper web on the paper resin, the former being added in the proportion of .225-2% and the latter of /42% based on the bone dry weight of the cellulose.

2. A method of preparing paper adapted for use as a base for photographic paper which includes the addition to the pulp slurry from which the paper is prepared for melamine formaldehyde resin and oxidized guar prior to forming the paper web on the paper resin, the former being added in the proportion of 1-2% and the latter of A -2% based on the bone dry weight of the cellulose.

3. A method of making paper adapted for use as a base for photographic paper which comprises adding to a pulp suspension in a beater an acid precipitable sizing material and an acidifying agent selected from the group consisting of aluminum chloride and aluminum sulfate to bring the suspension to a pH of 4-5, subsequently adding to the pulp suspension .225-2% of melamine formaldehyde resin and 2% of oxidized guar which percentages are based on the bone dry weight of the cellulose and forming a paper web on the paper resin from that pulp suspension.

4. A paper having high wet strength adapted for use as a base for photographic paper which contains melamine formaldehyde resin and oxidized guar, the former in the proportion of .225-2% and the latter of %-2% based on the bone dry weight of the cellulose.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,215,136 Schur Sept. 17, 1940 2,291,080 Hofierbert July 28, 1942 2,325,302 Britt July 2'7, 1944 2,338,602 Schur Jan. 4, 1944 2,502,520 Hansen Apr. 4, 1950 2,514,689 Woodward July 11, 1950 2,534,806 Webber et al. Dec. 19, 1950 2,548,513 Boughton Apr. 10, 1951 FOREIGN PATENTS Number Country Date 119,092 Australia Nov. 2, 1944 OTHER REFERENCES Broadbent et a1., World's Paper Trade Review, June 27, 1941, Tech. Sup., pages 49-56.

Collins, Paper Industry and Paper World, June 1943, pages 263-269.

Maxwell, Paper Trade Journal, May 13, 1943, pages 39-41.

Paper Industry and Paper World, December 1945, pages 1398, 1400, 1402 and 1404.

Swanson, TAPPI, February 1950, vol. 33, No. 2, pp. 77-81. 

1. A METHOD OF PREPARING PAPER ADAPTED FOR USE AS A BASE FOR PHOTOGRAPHIC PAPER WHICH INCLUDES ADDING TO THE PULP SLURRY FROM WHICH THE PAPER IS PREPARED MELAMINE FORMALDEHYDE RESIN AND OXIDIZED GUAR PRIOR TO FORMING THE PAPER WEB ON THE PAPER RESIN, THE OR BEING ADDED IN THE PROPORTION TO .225-2% AND THE LATTER OF 1/2-2% BASED ON THE NONE DRY WEIGHT OF THE CELLULOSE. 